An oxidized aromatic primary amino developing agent resulting from color development of color photographic silver halide light-sensitive material which has been exposed reacts with a coupler to form a dye, producing a dye image. In this process, color reproduction is usually carried out by the subtractive color process; to reproduce blue, green, and red, color images of yellow, magenta, and cyan which are, respectively, the complementary colors thereof are formed. In general, a magenta color image is formed using a pyrazolone, cyanoacetyl, or indazolone-based coupler.
In one of the most preferred embodiments of color photographic light-sensitive material, a coupler to form a dye image is introduced into a silver halide emulsion. This coupler is itself required to be nondiffusing or is prevented from diffusing by means of an emulsion binder matrix it is placed in.
Most conventional couplers which form a magenta color image are four equivalent couplers. Since, however, the amount of silver halide required by a two equivalent coupler in the formation of a dye is only one half of that needed by a four equivalent coupler, the two equivalent coupler is advantageous over the four equivalent coupler in that rapid processing of light-sensitive material becomes possible because the thickness of a light-sensitive layer can be decreased. Photographic properties are improved by a reduction in the film thickness, and production costs are decreased. Thus, many two equivalent couplers have been developed and are disclosed in a number of patents some of which are cited below.
Various 5-pyrazolone type couplers which form a magenta color image are known. With regard to substituents at the 3-position of the 5-pyrazolone ring, an alkyl group, an aryl group, an alkoxy group as described in U.S. Pat. No. 2,439,098, a ureido group as described in U.S. Pat. No. 3,558,319, an anilino group as described in U.S. Pat. No. 2,311,081 (reissue 22,329), a dialkylamino group as described in U.S. Pat. No. 3,615,506, and an acylamino group are known.
Several attempts have been made to convert 5-pyrazolone type couplers, which have heretofore been mainly used as magenta color-forming couplers, into two equivalent ones. For example, U.S. Pat. No. 3,214,437 and 3,253,924 disclose the introduction of a thiocyano group at the 4-position of the pyrazolone ring, and furthermore, U.S. Pat. Nos. 3,311,476, 3,419,391, 3,617,291, and 3,522,052 disclose the introduction of, respectively, an acyloxy group, an aryloxy group, a 2-triazolyl group, and a halogen atom at the 4-position of the pyrazolone ring.
These 4-substituted pyrazolone couplers, however, suffer from various disadvantages; for example, they cause color fog formation, their reactivity is not suitable, they are chemically instable and change with time into substances which can not form color, and they are difficult to synthesize.
It is also known, as described in U.S. Pat. No. 3,227,554, that the 5-pyrazolone ring can be substituted by an alkylthio group, an arylthio group, or a heterocyclic thio group at the 4-position thereof. However, many of the known thio-substituted pyrazolone compounds are not suitable for use in conventional color light-sensitive materials since their reactivity with the oxidation product of an aromatic primary amino color developing agent is improper or poor, and the mercapto compounds resulting from the coupling reaction thereof have a strong photographic aciton. Furthermore, their chemical stability is insufficient.
Recently, several 5-pyrazolone two equivalent magenta couplers having a heterocyclic substituent at the 4-position thereof have been developed. For example, West German Patent Laid-Open No. 2,536,191 discloses an imidazolyl group and its derivatives, a 1,2,4-triazolyl group and its derivatives, and a 1,2,3-triazolyl group and its derivatives, and West German Patent Laid-Open No. 2,651,363 discloses a 1,2,4-triazolyl group and its derivatives.
These compounds have fairly strong color-forming properties and satisfy a part of the characteristics required for two equivalent couplers. However, they are net yet sufficiently satisfactory; for example, couplers containing a imidazolyl group or a 1,2,4-triazolyl group sometimes cause a reduction in sensitivity through the mutual action thereof with silver halide (e.g., adsorption on light-sensitive nuclei).